1. Field of the Invention
This invention relates to a unique ophthalmic solution which is designed for general use in mammalian eyes but which is especially adapted for use in normalizing irregularly structured tear films in the eyes of humans and domestic animals. Thus, while the ophthalmic solution of this invention may be utilized generally as a carrier for ophthalmic medicaments, it will also be particularly useful when employed alone in the treatment of certain ophthalmologic conditions. For example, the present ophthalmic solution can serve as an artificial tear substance when administered to the eyes of patients whose tears are incorrectly structured and characterized by high sodium or potassium content as well as an aqueous volume significantly reduced from that of normal tears. The ophthalmic solution described herein is also effective as a lubricating agent for the eye following traumatic injury, exposure keratitis or surgery. In addition, this ophthalmic solution may be used to strengthen the tear films in the eyes of those who wear either hard or soft contact lenses.
2. Description of the Prior Art
Ophthalmic solutions have been previously developed for treating "dry eye" syndrome or for use as lubricating and cushioning agents for an eye subjected to traumatic injury or surgery. Such solutions have generally been isotonic, buffered to a required pH and contain various synthetic polymers as essential additives for improved viscosity and longer retention in the eye.
U.S. Pat. No. 3,767,788 to Rankin for example discloses one such solution which includes as an essential additive a high molecular weight ethylene oxide polyether, such as polyethylene oxide, along with other optional substituents, e.g. polyethylene glycol as a humectant, and various biocides and preservatives.
U.S. Pat. No. 3,907,985 to Rankin discloses another ophthalmic solution in a similar vein which is said to be effective in treating eye conditions such as dry eye but includes polystyrene sulfonate as an essential ingredient.
U.S. Pat. No. 4,039,662 to Hecht et al. describes an ophthalmic solution containing a particular polysaccharide and benzalkonium chloride which together apparently produce a synergistic effect and provide a synthetic tear film component which imparts a mucin-like layer to the cornea.
Since it has been commonly accepted in the art that isotonic levels of monovalent cation containing salts, principally sodium and potassium ions, are necessary to maintain tear films in a normal state, and thus prevent ocular discomfort or damage to the cornea and surrounding eye tissues, there is a clear indication in the abovementioned references and in other disclosures of the prior art that suitable ophthalmic solutions should incorporate relatively high levels of sodium ions, for example, to provide such solutions with a level of tonicity synonymous with body fluids. As will be described in greater detail below, it has now been discovered that an ophthalmic solution will be much more effective in restoring an irregularly structured tear film to its normal state if the amount of cationic salts, i.e. sodium salts, in the solution are controlled to a minimum level.